A Dual-Lunate-Ring Bulk RE-Ba-Cu-O Undulator

Design of hourglass nanoantenna for magnetic field enhancement

A passive DC magnetic concentrator is designed with transformation optics (TO) and realized by meta-materials. The passive DC magnetic concentrator based on space compression transformation can greatly enhance the magnetic field in a free space region and can be used for e.g., improving the sensitivity of magnetic sensors and increasing the efficiency of wireless energy transmission. The magnetic property of the medium obtained by TO is extremely anisotropic. To solve this, we use magnetic metamaterials made of alternated high-permeability ferromagnetic (HPF) materials and high-temperature superconductor (HTS) materials. We optimize our structure by conducting simulations using the finite element method (FEM) and experimentally demonstrate a strong, 4.74-time enhancement of the DC magnetic field by our meta-material magnetic concentrator. We also demonstrate that a simplified structure with only HPF materials working at room temperature can still gives 3.84-time enhancement of the DC magnetic field. The experimental results are in good agreement with the numerical simulations based on FEM.

In this article, we introduce a new optical energy focusing structure consisting of a circular dielectric Bragg nanocavity and a circular metallic plasmonic lens. Via the hybridization of Bragg cavity modes and surface plasmon modes, optical energy is highly confined in the central region of the Bragg nanocavity under linearly polarized illumination. When either a bowtie nano-antenna (BNA) or a magnetic resonator (MR) is placed on this focusing structure, the energy can be high-efficiently coupled and focused into the BNA or MR. Simulations show that the electric field enhancement (|E|/|E0|) in the BNA and magnetic field enhancement (|H|/|H0|) in the MR can be more than 3000 and 200, respectively. This proposed hybrid dielectric-metallic structure opens a new avenue in energy focusing and transferring and provides opportunities for various applications, including single-molecule SERS, optical trapping, photolithography, fluorescent microscopy, magnetic sensors, etc.

Transport properties of double quantum wires in magnetic field

Dual-mode coupling resonance and dynamic stability of axially moving ferromagnetic thin plate strips in alternating magnetic field

The aim of the present paper is to investigate the radiation absorption and diffusion thermo on unsteady magneto hydrodynamic flow past an infinite vertical permeable moving plate in the presence of thermal radiation, heat absorption and homogenous chemical reaction, subjected to variable suction. The plate is assumed to be embedded in a uniform porous medium and moves with a constant velocity in the flow direction in the presence of a transverse magnetic field. The equations governing the flow are transformed into a system of nonlinear ordinary differential equations by using perturbation technique. Graphical results for the velocity distribution, temperature distribution and concentration distribution based on the numerical solutions are presented and discussed. Also we discuss the effects of various parameters on the skin-friction coefficient and the rate of heat transfer in the form of Nusselt number and rate of mass transfer in the form of Sherwood number at the surface. Velocity and temperature distribution is observed to increase with an increase in radiation absorption and Dufour parameter, whereas it diminishes with the enhancement in magnetic field, heat absorption coefficient, radiation parameter and chemical reaction parameter with respect to velocity, temperature and concentration distributions.

Nanoscale magnetic systems play a decisive role in areas ranging from biology to spintronics. Although, in principle, THz electron paramagnetic resonance (EPR) provides high-resolution access to their properties, lack of sensitivity has precluded realizing this potential. To resolve this issue, the principle of plasmonic enhancement of electromagnetic fields that is used in electric dipole spectroscopies with great success is exploited, and a new type of resonators for the enhancement of THz magnetic fields in a microscopic volume is proposed. A resonator composed of an array of diabolo antennas with a back-reflecting mirror is designed and fabricated. Simulations and THz EPR measurements demonstrate a 30-fold signal increase for thin film samples. This enhancement factor increases to a theoretical value of 7500 for samples confined to the active region of the antennas. These findings open the door to the elucidation of fundamental processes in nanoscale samples, including junctions in spintronic devices or biological membranes.

Sub wavelength all-dielectric structures processing simultaneously electric and magnetic resonances provide a new horizon for tailoring magnetic light–matter interaction that is often overlooked in optical spectrum. In general, the magnetic field enhancement can be boosted by utilizing the magnetic resonances of dielectric resonators where structural disorder effect is considered as a parasitic negative effect for the targeted response. Here, in contrast, we theoretically propose and experimentally demonstrate that compact disordered dielectric resonators with substantial enhancement of free-space magnetic field can be automatically designed by the combination of simulated annealing algorithm and numerical solution of Maxwell’s equations, providing an alternative for tailoring magnetic light–matter interaction. The functionality and reliability of the proposed concept are further verified by microwave experiment. Our results might facilitate the application of compact disordered magnetic resonators in enhancing magnetic dipole transition of quantum emitter, magnetic resonance imaging, wireless power transfer and beyond.

It is the first time that the magnetic field enhancement (MFE) is used to study the interaction of magnetic resonators (MRs), which is more sensitive than previous parameters–shift and damping of resonance frequency. To avoid the coherence of lattice and the effect of Bloch wave, the interaction is simulated between two MRs with same primary phase when the distance is changed in the range of several resonance wavelengths, which is also compared with periodic structure. The calculated MFE oscillating and decaying with distance with the period equal to resonance wavelength directly shows the retardation effect. Simulation also shows that the interaction at normal incidence is sensitive to the phase correlation which is related with retardation effect and is ultra-long-distance interaction when the two MRs are strongly localized. When the distance is very short, the amplitude of magnetic resonance is oppressed by the strong interaction and thus the MFE can be much lower than that of single MR. This study provides the design rules of metamaterials for engineering resonant properties of MRs.

The interaction between chiral molecules and circularly polarized light is largely influenced by the local optical chirality density. This interaction prompts substantial demand of the design of nanophotonic platforms capable of enhancing such effects across large and accessible volumes. Such a magnification requires nanostructures that provide strong electric and magnetic field enhancements while preserving the phase relation of circular light. Dielectric nanostructures, particularly those able to support resonances, are ideal candidates for this task due to their capacity for high electric and magnetic field enhancements. On the other hand, efficient third harmonic generation requires strong electric field resonances within dielectric materials, a feature often boosted by incorporating plasmonic materials into hybrid systems. In this work, we numerically propose a coupled silicon disk-gold ring system that can exploit the anapole-induced field confinement to provide a broadband magnified circular dichroism under realistic conditions, reaching values up to a 230-fold enhancement. We also demonstrate that this structure can be employed as an efficient third harmonic generator, which, when integrated with chiral media, enables an 800-fold enhancement in circular dichroism. Furthermore, we show that pulsed illumination at intensities up to 10 GW/cm2 does not induce temperature increments that could potentially damage the samples. These findings suggest that this system can be a promising and versatile approach toward ultrasensitive chiral sensing.

Optical toroidal dipole and electromagnetic field enhancement have attracted much interest owing to their interesting physical features and various potential nanophotonic applications. In this paper, novel antireflective nanofocusing methods to deliver and squeeze toroidal dipole moment with simultaneous enhancement of electric and magnetic fields are suggested. By coupling the two fundamental modes of a metal–insulator–metal waveguide with a partial mirror in a waveguide and a nanocavity, resonant squeezing of longitudinal and perpendicular toroidal dipoles in an ultracompact nanocavity (∼ λ 2 / 190) is achieved at the near-telecom wavelengths. Moreover, electric and magnetic field enhancements occur simultaneously in a designated nanocavity. We expect that the proposed scheme would pave a way to engineer nanophotonic waveguide based light-matter interactions by enhancing both electric and magnetic fields. This study would interest both nanophotonics and quantum optics communities.

In this paper an excitation of waves is considered during the time interval in which the undisturbed magnetic field changes its direction. If this interval is taken to be 2 years, which is shorter than the 11-year cycle, then the undisturbed components of the magnetic field may be linearly dependent on time and independent of the coordinates. The excitation of waves is due to the undisturbed stationaryV 0 flow with divV 0 = 0 and with (V 0 rot0) = constant. We use the local Cartesian coordinate system, which is immovable towards the solar centre, and consider the case when the toroidal component of the undisturbed magnetic field changes its sign simultaneously with one of the axial components. The third component does not change its direction. The efficiency of the enhancement of the magnetic field and velocity disturbances depends on the Alfven wave frequency,ω A. Whenω A = 0, the component of the disturbed velocity, which is directed along the constant component of the undisturbed magnetic field, increases. In this case the shear waves excite the carrier (high) frequency (KV 0), whereK is the wave vector. Due to the shear instability the amplitude of the velocity increases during 1 year before the moment of reversal of the global magnetic field polarity (RGMFP) for an arbitrary latitude. It reaches a maximum at RGMFP and decreases in the next year. Whenω A > 0, then the amplitudes of the disturbed values reach maxima before the moment of RGMFP, and whenω A < 0, they reach maxima after it. We argue that the shear waves propagate from middle latitudes to the pole and equator. Using the results of the analytical solutions and leaning on the evidence of the observational data (Gigolashvili and Japaridze, 1992), we derive the result that the component of the undisturbed magnetic field, which is perpendicular to the solar surface, changes its sign simultaneously with the toroidal component.

Mössbauer effect study of the internal magnetic field in small iron particles

Silver nanoparticles (AgNPs) are incredibly versatile nanostructures that more recently have been exploited to create advanced optoelectronic materials due enhancement of local magnetic field after its irradiation. However, the use of AgNPs as nanoantennas to amplify photophysical properties of close photosensitizer (PS) molecules in photodynamic therapy is still underexplored. The reason for that is the difficulty to control crucial parameters such as silver-PS distance in aqueous solution. In this scenario, here we propose a nanohybrid system where AgNP/PS distance is controlled by a thin layer of different Pluronic copolymers. The controllable distance and aqueous stability of proposed nanohybrids allow a tunable enhancement of fluorescence emission and singlet oxygen generation of some selected PS molecules. A detailed mechanism investigation demonstrated that the observed metal-enhanced photophysics is due to magnetic field enhancement close to AgNP surface (AgNP/PS distance-controlled effect) and the resonant coupling of AgNP hot electrons and HOMO-LUMO energies of the PS (AgNP/PS spectral overlap-controlled effect). These results show that the rational design in engineering new nanohybrid structures allowed photophysical improvement of PS molecules in aqueous solution in a tunable way and point out Pluronic-based AgNP/PS nanohybrids as a smart material for further developments aiming at theranostic applications in photodynamic therapy.

We present hydrodynamic and magnetohydrodynamic (MHD) simulations of liquid sodium flow with the PLUTO compressible MHD code to investigate influence of magnetic boundary conditions on the collimation of helicoidal motions. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multiblades impeller inspired by those used in the Von-Kármán-sodium (VKS) experiment. We show that the impinging of the large-scale flow upon the impeller generates a coherent helicoidal vortex inside the blades, located at a distance from the upstream blade piloted by the incident angle of the flow. This vortex collimates any existing magnetic field lines leading to an enhancement of the radial magnetic field that is stronger for ferromagnetic than for conducting blades. The induced magnetic field modifies locally the velocity fluctuations, resulting in an enhanced helicity. This process possibly explains why dynamo action is more easily triggered in the VKS experiment when using soft iron impellers.